1. Field of the Invention
The present invention relates to a scroll compressor which is built into an air conditioner, refrigerating machine, or the like, and in particular, relates to the shape of scroll members therein.
2. Description of the Related Art
FIG. 8 is a cross-sectional view of a well-known scroll compressor. This scroll compressor comprises a fixed scroll member 101 which is fixedly attached to a housing 100 and a revolving scroll member 102 which is revolutionarily freely supported in the housing 100.
The fixed scroll member 101 has a fixed end plate 101a and a spiral wall 101b, and the revolving scroll member 102 has a revolving end plate 102a and a spiral wall 102b. The fixed and revolving scroll members 101 and 102 face each other in a manner such that the spiral walls 101b and 102b are engaged with each other with a phase difference of 180xc2x0, and the revolving scroll member 102 is made to revolve around the axis of the fixed scroll member 101 via the shaft 103, so that the capacities of compression chambers, which are formed between the spiral walls 101b and 102b, are gradually reduced and the fluid in the compression chambers is compressed, thereby finally discharging the high-pressure fluid from a discharge port 104 which is provided in a center portion of the fixed end plate 101a. 
In this scroll compressor, the capacity of a crescent-shaped closed space formed at the outermost area of the spiral corresponds to the capacity for the introduced fluid which is gradually compressed. Therefore, in order to increase the capacity for the introduced fluid, that is, the capacity for the fluid to be compressed, the number of coils (or turns) of the spiral must be increased, or alternatively, the height of the spiral walls must be increased.
However, an increase in the number of turns of the spiral leads to an increase in the diameter of the compressor, and an increase in the height of the spiral walls causes a decrease in the rigidity of the spiral walls relative to the pressure of the compressed fluid.
Japanese Patent No. 1296413 (refer to Japanese Examined Patent Application, Second Publication No. Sho 60-17956) discloses an example structure for solving these problems. FIGS. 6A and 6B are perspective views which respectively show a fixed scroll member 1 and a revolving scroll member 2 employed in this example. The fixed scroll member 1 has an end plate 1a and a spiral wall 1b which is formed on a face of the end plate 1a. Similarly, the revolving scroll member 2 has an end plate 2a and a spiral wall 2b which is formed on a face of the end plate 2a. In the above faces of the end plates 1a and 2a, step portions 3 and 3 are each formed, and in each step portion 3, the side closer to the center of the spiral is higher than the side closer to the outer end of the spiral. In addition, step portions 4 and 4 corresponding to the step portions 3 and 3 are each formed in the upper ends of the spiral walls 1b and 2b of the scroll members 1 and 2. In each step portion 4, the side closer to the center of the spiral is lower than the side closer to the outer end of the spiral.
Therefore, the above-explained scroll compressor has a feature that the spiral walls and end plates are respectively formed to have step portions, that is, in the spiral walls, the outer side (of the spiral) is higher and the center side is lower, while in the end plates, the outer side is lower and the center side is higher so as to correspond to the spiral walls.
FIG. 7 shows the engagement state in which the spiral walls 1b and 2b are engaged with each other with a phase difference of 180xc2x0. As shown in the figure, compression chambers C2 and C3 and the like are formed between the spiral walls 1b and 2b, by the end plates and/or the slide planes of the step portions of the end plates and spiral walls. In this state, when the revolving scroll member 2 revolves around the axis of the fixed scroll member 1, the capacities of the compression chambers gradually decrease, thereby compressing the relevant fluid.
In the above scroll compressor, the height of the compression chamber closer to the outer side of the spiral is relatively high; thus, the capacity for the introduced fluid can be increased without increasing the outer diameter of the compressor. In addition, the height of the compression chamber closer to the center can be low, so that high rigidity of the walls can be obtained.
However, in comparison with general scroll compressors having walls of a uniform height, each step portion 3 and the corresponding step portions 4 partially slide on each other, that is, the engagement of the step portions occurs. Therefore, even if a very slight gap between the engaged portions exists due to the working or assembling tolerance of the scroll members, the fluid may leak through the gap, and thus the compression efficiency is reduced.
In addition, in order to solve the above problem, the scroll members should be manufactured to a very high accuracy; thus, the productivity is very low and the manufacturing cost is very high.
In consideration of the above circumstances, the present invention relates to scroll compressors, which comprise scroll members having step portions, and an object of the present invention is to provide a scroll compressor for reducing leakage of the fluid occurring at the step portions as much as possible and improving the compression efficiency. Another object of the present invention is to provide a scroll compressor which has less leakage of the fluid and can realize a high compression efficiency without increasing the precision in the manufacture of the scroll members.
Therefore, the present invention provides a scroll compressor comprising:
a fixed scroll member which has an end plate and a spiral wall provided on a face of this end plate and is fixed as a specific position; and
a revolving scroll member which has an end plate and a spiral wall provided on a face of this end plate and is supported in a manner such that the spiral walls are engaged with each other and the revolving scroll member can revolve while rotation is prohibited, wherein:
the face of each scroll member, on which the spiral wall is provided, is divided into a plurality of areas which include a high portion closer to the center of the spiral, an adjacent low portion closer to the outer end of the spiral, and a step portion formed at the boundary of the high and low portions, where the high portion is higher than the low portion;
the edge of each spiral wall has a low edge which corresponds to the high portion and is closer to the center of the spiral, a high edge which corresponds to the low portion and is closer to the outer end of the spiral, and a step portion formed at the boundary of the high and low edges;
when the scroll members are engaged with each other, the end plates, the spiral walls, and the step portions partially contact with each other, so that closed spaces are generated between the scroll members;
the revolving scroll member is made to revolve so that the closed spaces gradually move from the outer side to the center side of the spiral and the capacities of the closed spaces are gradually reduced and a fluid in the closed spaces is compressed;
between the engaged scroll members, a high-pressure space which communicates with a discharge chamber is formed close to the center of the spiral, and among contact points at which the spiral walls of both scroll members contact with each other immediately before the innermost closed space communicates with the high-pressure space, the innermost contact point is defined as a base point;
the angular distance from the base point to the outer end of each spiral wall, measured along the inner-peripheral face of the spiral wall, is approximately 4xcfx80 rad; and
the angular distance from the base point to the step portion of each end plate, measured along the inner-peripheral face of the corresponding spiral wall, is equal to or more than approximately 3xcfx80 rad.
According to the above structure, each step portion can be placed in a preferable area of the scroll members. Therefore, it is possible that after the moment when the innermost closed space (called the first closed space) communicates with the high-pressure space (which communicates with the discharge chamber), the step portions do not participate in the formation of the first closed space. The high-pressure fluid reversely flows from the high-pressure space due to the communication of the first closed space with the high-pressure space, and the pressure of the fluid in the first closed space increases. Accordingly, even when the differential pressure between the first closed space and the second closed space (which is adjacent to the first closed space and is placed closer to the outer end of the spiral) increases, the step portions do not participate in the formation of the first closed space; thus, the leakage of the fluid due to the presence of the step portions can be avoided. That is, the step portions may participate in the formation of the second closed space or more distant closed spaces, thereby reducing the leakage of the fluid due to the presence of the step portions as much as possible and improving the compression efficiency. Such an improved compression efficiency can be realized without improving the precision in the manufacture of the scroll members.